Existing compact weighing apparatus generally use so-called parallelogram type load cells, in which, as shown in FIG. 1, the strain gauges 1B are mounted on the elastic flexible fulcrum portions 1c of a parallelogram mechanism 1A. The external configuration of mechanism 1A is in the shape of a parallelogram having equal-length upper and lower beams 1a and 1b, and equal-length right and left vertical members 1d and 1e which connect the upper and lower beams at a prescribed interval via portions 1c provided at both ends of each of the upper and lower beams.
In order to perform accurate weight measurement using a load cell system or other high-precision weighing apparatus, the support surface on which the weighing apparatus is installed should be stable and stationary so that it does not impart vibrations to the load cell or reflect vibrations caused by the weighing apparatus.
Nevertheless, with the exception of some special locations, the installation surfaces used to support such weighing apparatus generally vibrate as the result of vibration caused by vehicles passing nearby, factory machinery, etc. As a result when a weighing apparatus is installed on an unstable support surface subject to vibration and the material to be weighed is loaded onto the loading tray (pan, table, platform, etc.) of the weighing apparatus, the weight signal of the weighing apparatus is adversely affected by the vibration transmitted from the support surface.
Also, for a weighing apparatus in which load cells are used, the vibration from the support surface of the apparatus or the vibration of a part of the apparatus is transmitted to and through the weighing apparatus, and this mechanical vibration is converted into an electrical signal appearing as electrical noise. Because this noise consists mostly of relatively low-frequency (frequencies of approximately 7 Hz or less) components, it is difficult to eliminate. Even if mechanical dampers are used and an active filter or other device is installed in series with the signal amplifier, the present state of the art has difficulty in finding a way to deal with this noise problem. The larger the mass of the tare, such as the loading tray, the more the weight measurement is affected and the more severe the problem becomes.
Lowering of the effective frequency range at which filtering may be performed by a low-pass filter can generally be considered as an effective means of dealing with the problem. However, low pass filtering results in a delay of the weight signal, thus reducing the responsiveness of the weighing apparatus. This reduction in responsiveness is in direct oppostion to achieving an increase in the weight measurement speed, which is one of the objectives in improving today's weighing apparatus.